sigmalowHunting

MaxMpxCt Registry Value Changed

Detects changes to the "MaxMpxCt" registry value. MaxMpxCt specifies the maximum outstanding network requests for the server per client, which is used when negotiating a Server Message Block (SMB) connection with a client. Note if the value is set beyond 125 older Windows 9x clients will fail to negotiate. Ransomware threat actors and operators (specifically BlackCat) were seen increasing this value in order to handle a higher volume of traffic.

MITRE ATT&CK

T1070.005

defense-evasion

Detection Query

selection:
  TargetObject|endswith: \Services\LanmanServer\Parameters\MaxMpxCt
condition: selection

Author

Nasreddine Bencherchali (Nextron Systems)

Created

2024-03-19

Data Sources

windowsRegistry Set Events

Platforms

windows

References

Tags

attack.defense-evasionattack.t1070.005

Raw Content

title: MaxMpxCt Registry Value Changed
id: 0e6a9e62-627e-496c-aef5-bfa39da29b5e
status: test
description: |
    Detects changes to the "MaxMpxCt" registry value.
    MaxMpxCt specifies the maximum outstanding network requests for the server per client, which is used when negotiating a Server Message Block (SMB) connection with a client. Note if the value is set beyond 125 older Windows 9x clients will fail to negotiate.
    Ransomware threat actors and operators (specifically BlackCat) were seen increasing this value in order to handle a higher volume of traffic.
references:
    - https://www.huntress.com/blog/blackcat-ransomware-affiliate-ttps
    - https://securityscorecard.com/research/deep-dive-into-alphv-blackcat-ransomware
    - https://www.intrinsec.com/alphv-ransomware-gang-analysis/?cn-reloaded=1
    - https://www.sentinelone.com/labs/blackcat-ransomware-highly-configurable-rust-driven-raas-on-the-prowl-for-victims/
author: Nasreddine Bencherchali (Nextron Systems)
date: 2024-03-19
tags:
    - attack.defense-evasion
    - attack.t1070.005
logsource:
    category: registry_set
    product: windows
detection:
    selection:
        TargetObject|endswith: '\Services\LanmanServer\Parameters\MaxMpxCt'
    condition: selection
falsepositives:
    - Unknown
level: low